This invention relates generally to the chemical-mechanical polishing (CMP) of metal substrates on semiconductor wafers and slurry compositions therefor. In particular, the present invention relates to a CMP slurry composition which is characterized to enhance removal of barrier layer materials and low-k dielectric materials in relation to PETEOS dielectric layer materials and copper, and to provide tunability for the selective removal of barrier layer materials, copper, low-k dielectric materials, and PETEOS dielectric layer materials, during CMP processing of substrates comprised of metal, barrier layer materials, and dielectric layer materials. This invention is especially useful for metal CMP and most especially for step 2 copper CMP processes.
Chemical mechanical planarization (chemical mechanical polishing, CMP) for planarization of semiconductor substrates is now widely known to those skilled in the art and has been described in numerous patents and open literature publications. Some introductory references on CMP are “Polishing Surfaces for Integrated Circuits”, by B. L. Mueller and J. S. Steckenrider, Chemtech, February, 1998, pages 38-46; and “Chemical-Mechanical Polish” by G. B. Shinn et al., Chapter 15, pages 415-460, in Handbook of Semiconductor Manufacturing Technology, editors: Y. Nishi and R. Doering, Marcel Deicker, New York City (2000).
In a typical CMP process, and in the process useful with the current invention, a substrate (e.g., a wafer) is placed in contact with a rotating polishing pad attached to a platen. A CMP slurry, typically an abrasive and chemically reactive mixture, is supplied to the pad during CMP processing of the substrate. Alternatively, a portion or all of the abrasive material can be disposed on the polishing pad. During the CMP process, the pad (fixed to the platen) and substrate are rotated while a wafer carrier system or polishing head applies pressure (downward force) against the substrate. The slurry accomplishes the planarization (polishing) process by chemically and mechanically interacting with the substrate film being planarized due to the effect of the downward force and the rotational movement of the pad relative to the substrate. Polishing is continued in this manner until the desired film on the substrate is removed with the usual objective being to effectively planarize the substrate. Typically metal CMP slurries contain an abrasive material, such as silica or alumina, suspended in an oxidizing, aqueous medium.
Silicon based semiconductor devices, such as integrated circuits (ICs), typically include at least one dielectric layer, metal wires and interconnects, and optionally one or more specialized layers such as diffusion barriers. Multilevel circuit traces, typically formed principally from aluminum, an aluminum alloy, copper, or a copper alloy are patterned onto the dielectric layer substrate. CMP processing is often employed to remove and planarize excess metal at different stages of semiconductor manufacturing. For example, one way to fabricate a multilevel copper interconnect or planar copper circuit traces on a dielectric substrate is referred to as the damascene process. In a semiconductor manufacturing process typically used to form a multilevel copper interconnect, metallized copper lines or copper vias are formed by electrochemical metal deposition followed by copper CMP processing. In a typical process, the interlevel dielectric (ILD) surface is patterned by a conventional dry etch process to form vias and trenches for vertical and horizontal interconnects and make connection to the sublayer interconnect structures. The patterned ILD surface typically is coated with an adhesion-promoting layer such as titanium or tantalum and/or a diffusion barrier layer such as titanium nitride or tantalum nitride over the ILD surface and into the etched trenches and vias. The adhesion-promoting layer and/or the diffusion barrier layer is then overcoated with copper, for example, by a seed copper layer and followed by an electrochemically deposited copper layer. Electro-deposition is continued until the structures are filled with the deposited metal. Finally, CMP processing is used to remove the copper overlayer, adhesion-promoting layer, and/or diffusion barrier layer, until a planarized surface with exposed elevated portions of the dielectric (silicon dioxide and/or low-k) surface is obtained. The vias and trenches remain filled with electrically conductive copper forming the circuit interconnects. The adhesion-promoting layer plus diffusion barrier layer is typically collectively referred to as the “barrier layer.”
The dielectric layer comprises, for example, SiO2 (doped or undoped with dopants such as boron or phosphorous), possibly with a layer of silicon nitride. Alternatively, interlevel dielectric layers may comprise, for example, an oxide, FSG, PSG, BPSG, PETEOS, HDP oxide, a silicon nitride, silicon oxynitride, silicon carbide, silicon carbo-oxynitride, a low dielectric constant material (for example, SILK, porous SiLK, teflon, low-K polymer (possibly porous), aerogel, xerogel, BLACK DIAMOND, HSQ, or any other porous glass material or a combination or stack thereof.
Not all dielectric materials respond equally to various CMP compositions and parameters. A commonly used dielectric material include “PETEOS”, an SiO2 film formed from tetraethyl-orthosilicate by chemical vapor deposition using plasma as a promoter. Commonly used lower dielectric constant materials generally have a dielectric constant below 3.0 and are generally referred to as “low-K dielectrics,” which typically provide a carbon component and/or a porous component, and include commercial products such as: “SiLK”™, available from Dow Chemical Company, NY, USA; FLARE™, available from Honeywell, N.J., USA; microporous glasses such as Nanoglass™ (Porous SiO2), available from Honeywell, Inc., NJ, USA; Black Diamond™ (Carbon-doped SiO2), available from Applied Material, Calif., USA; Coral™ (Silicon carbide based dielectrics), available from Novellus Systems, Inc., CA, USA; and Xerogel, available from Allied Signal, N.J., USA.
A thin dielectric layer may be formed over an interlevel dielectric layer, which comprises, for example, silicon nitride, silicon carbide, SiCNO or a silicon oxide (for example, a high-density plasma oxide).
In addition, an added diffusion barrier/etch stop may be included near the top surface of a dielectric layer, such as AlOx, AlN, Si3N4, TiO2, ZrO2, or TaOx that would be deposited after the barrier layer planarization process. This diffusion barrier is particularly useful if damascene processes are used to create the via or metallization to the contact.
Formation of metal structures which are situated above the contacts is considered to be part of the back end processes. The back end process steps may be those standard in the semiconductor industry. The metallization may be, for example, either Al or Cu based. The Al is preferably etched while the Cu is preferably used in a damascene approach. However, etching Cu and Al formed in a damascene process is also possible. An exemplary aluminum metallization will preferably have CVD tungsten plugs or Al plugs, and the Al will preferably be Cu-doped for improved electromigration resistance. Metal diffusion barriers for Al may include, for example, TiN and/or Ti. Exemplary copper metallization may have, for example, Cu or W plugs with either Ti, TiN (titanium nitride), TiSiN, Ta, tantalum nitride, and/or TaSiN diffusion barriers.
The interconnects and the metal lines preferably comprise the same material. Plugs and conductors comprise a metal material, for example, copper, aluminum, titanium, TiN, tungsten, tungsten nitride, or any combination or stack thereof. A barrier/liner may be formed between the plug and the respective interlevel dielectric layer. If formed, the barrier/liner layer comprises, for example, Ti, TiN, W, tungsten nitride, Ta, tantalum nitride, any conventional barrier/liner layer, or any combination or stack thereof).
In addition, various metals and metal alloys have been used at different stages of semiconductor manufacturing, and an exemplary selection of metals which may be contacted by a polishing process include tungsten, aluminum, copper, tantalum, tantalum nitride, titanium, titanium nitride, ruthenium, platinum, iridium, and combinations thereof. Other structures can also be present, providing other materials such as one or more noble metals, polysilicon, silicon nitride, and other minerals, metals, and compounds. For a typical wafer undergoing copper damascene process, the insulating layers typically comprise silica, silicon nitride, and low-k films including carbon-doped oxides; the barrier layers disposed between copper and dielectric material typically comprise Ta, TaN, Ti, TiN, or various mixtures and combinations thereof.
A multi-step copper CMP process may be employed to achieve local and global planarization in the production of IC chips, referred to as a step 1 copper CMP process, followed by a barrier layer CMP process. In relation to copper CMP, the current state of this technology involves use of a two-step process. During step 1 of a copper CMP process, the overburden copper is removed and planarized. Then step 2 of the copper CMP process follows to remove the barrier layer materials and achieve both local and global planarization. The barrier layer CMP process is frequently referred to as a barrier or step 2 copper CMP process. The ratio of the removal rate of copper to the removal rate of dielectric material is called the “selectivity” for removal of copper in relation to dielectric material during CMP processing of substrates comprised of copper, barrier layer materials, and dielectric material. The ratio of the removal rate of barrier layer materials to the removal rate of copper is called the “selectivity” for removal of barrier layer materials in relation to copper during CMP processing of substrates comprised of copper, barrier layer materials, and dielectric materials. Barrier layer materials include tantalum, tantalum nitride, tungsten, noble metals such as ruthenium and ruthenium oxide, and combinations thereof.
When CMP slurries over-polish copper layers they may create a depression or “dishing” effect in the copper vias and trenches. This feature distortion is unacceptable due to lithographic and other constraints in semiconductor manufacturing. Another feature distortion that is unsuitable for semiconductor manufacturing is called “erosion.” Erosion is the topography difference between a field of dielectric and a dense array of copper vias or trenches. In CMP, the materials in the dense array may be removed or eroded at a faster rate than the surrounding field of dielectric. This causes a topography difference between the field of dielectric and the dense copper array.
A number of systems for CMP of copper have been disclosed. A few illustrative examples are listed next. Kumar et al. in an article entitled “Chemical-Mechanical Polishing of Copper in Glycerol Based Slurries” (Materials Research Society Symposium Proceedings, 1996) disclose a slurry that contains glycerol and abrasive alumina particles. An article by Gutmann et al. entitled “Chemical-Mechanical Polishing of Copper with Oxide and Polymer Interlevel Dielectrics” (Thin Solid Films, 1995) discloses slurries based on either ammonium hydroxide or nitric acid that may contain benzotriazole (BTA) as an inhibitor of copper dissolution. Luo et al. in an article entitled “Stabilization of Alumina Slurry for Chemical-Mechanical Polishing of Copper” (Langmuir, 1996) discloses alumina-ferric nitrate slurries that contain polymeric surfactants and BTA. Carpio et al, in an article entitled “Initial Study on Copper CMP Slurry Chemistries” (Thin Solid Films, 1995) disclose slurries that contain either alumina or silicon particles, nitric acid or ammonium hydroxide, with hydrogen peroxide or potassium permanganate as an oxidizer.
Generally, after removal of overburden copper in step 1, polished wafer surfaces have non-uniform local and global planarity due to differences in the step heights at various locations of the wafer surfaces. Low density features tend to have higher copper step heights whereas high density features tend to have low step heights. Due to differences in the step heights after step 1, selective slurries are highly desirable for step 2 copper CMP for the selective removal of barrier layer materials in relation to copper and for the selective removal of dielectric materials in relation to copper.
Chemical mechanical polishing slurries have two actions, a chemical component and a mechanical component. In the case of CMP of most metals, the chemical action is generally considered to take one of two forms. In the first mechanism, the chemicals in the solution react with the metal layer to continuously form an oxide layer on the surface of the metal. This generally requires the addition of an oxidizer such as hydrogen peroxide, ferric nitrate, etc to the solution. Then the mechanical abrasive action of the particles continuously and simultaneously removes this oxide layer. A judicious balance of these two processes obtains optimum results in terms of removal rate and polished surface quality. In the second mechanism, no protective oxide layer is formed. Instead, the constituents in the solution chemically attack and dissolve the metal, while the mechanical action is largely one of mechanically enhancing the dissolution rate by such processes as continuously exposing more surface area to chemical attack, raising the local temperature (which increases the dissolution rate) by the friction between the particles and the metal and enhancing the diffusion of reactants and products to and away from the surface by mixing and by reducing the thickness of the boundary layer.
There are a number of theories as to the mechanism for chemical mechanical polishing of copper. An article by Zeidler et al. (Microelectronic Engineering, 1997) proposes that the chemical component forms a passivation layer on the copper changing the copper to a copper oxide. The copper oxide has different mechanical properties, such as density and hardness, than metallic copper and passivation changes the polishing rate of the abrasive portion. The above article by Gutmann et al. suggests that the mechanical component abrades elevated portions of copper, and the chemical component then dissolves the abraded material. The chemical component may also passivate recessed copper areas minimizing dissolution of those portions.
Various U.S. patents and published applications that mention some form or sulfonic acids in a CMP system include:
U.S. Pat. Nos. 6,527,622 and 6,852,632, and U.S. Patent Publication No. 2003/0181142, each describing a CMP slurry for noble metal;
U.S. Pat. No. 6,750,128 describing a CMP slurry for copper/barrier materials comprising hydrogen peroxide and e.g., nitrobenzene sulfonic acid;
U.S. Patent Publication No. 2004/0173574, No. 2003/0203624 and 2004/0235407 describe a chemical metal polishing composition comprising an oxidizer which is an organic nitro compound, e.g., m-nitrobenzene sulfonic acid.
U.S. Patent Publication No. 2005/0090109 describing a CMP composition comprising an organosulfonic acid oxidizer, wherein the fluid composition can further comprise an abrasive and a hydroxylamine compound;
U.S. Pat. No. 6,117,784 describing a method of etching the exposed copper seed layer not covered by the electroplated or electrolessly plated copper using an etchant that preferentially etches said copper seed layer at a rate higher than that for the electroplated or electrolessly plated metal; and wherein said etchant comprises a persulfate, a surfactant, and optionally further contains stabilized 1-5% hydrogen peroxide and a sulfur-containing compound such as benzene sulfonic acid;
U.S. Pat. No. 6,740,589 describing a CMP composition for polishing copper and a barrier comprising an aqueous solvent, an amino acid having two or more nitrogen atoms, and a copper-polishing accelerator selected from the group consisting of a large number of inorganic acids and organic acids, one of which is benzenesulfonic acid. The polishing composition optionally contains an oxidizing agent such as hydrogen peroxide;
A number of applications describes CMP compositions having an oxidizer, e.g., hydrogen peroxide, and a sulfonic acid (e.g., para-toluene sulfonic acid) or a anionic sulfonate-containing surfactant (e.g., dodecyl-benzene sulfonic acid or alkyl-benzene sulfonic acids). Included are U.S. Patent Publication Nos. 2004/0014413; 2004/0063391; 2004/0162011; 2004/0166779; 2004/0266326; 2005/0026444; 2004/0132305; 2003/0196386; and also U.S. Pat. No. 6,786,944.